Which statement best defines an acute triangle?

Which statement best defines an acute triangle?

• A. One angle is 90 degrees.
• B. All interior angles are less than 90 degrees.
• C. All three sides are equal.
• D. Two sides are congruent.

Answer: (B)

An acute triangle is defined by its angles: every interior angle is less than 90 degrees. The sum of angles in any triangle is 180 degrees, so having all three angles under 90 is possible and characterizes an acute triangle. A right triangle has one angle equal to 90 degrees, which is not acute. An equilateral triangle has all three sides equal, which guarantees all angles are 60 degrees, making it acute, but that’s a property about sides, not the defining angle condition. An isosceles triangle has two equal sides and can be acute, right, or obtuse depending on its angles. So the statement that all interior angles are less than 90 degrees is the defining description of an acute triangle.

An acute triangle is defined by its angles: every interior angle is less than 90 degrees. The sum of angles in any triangle is 180 degrees, so having all three angles under 90 is possible and characterizes an acute triangle. A right triangle has one angle equal to 90 degrees, which is not acute. An equilateral triangle has all three sides equal, which guarantees all angles are 60 degrees, making it acute, but that’s a property about sides, not the defining angle condition. An isosceles triangle has two equal sides and can be acute, right, or obtuse depending on its angles. So the statement that all interior angles are less than 90 degrees is the defining description of an acute triangle.